Mo and Cu (which may be referred to as copper hereinafter) are not dissolved into each other in a solid state. Therefore, a Mo—Cu based material generally is a composite material obtained by mixing and bonding these components together. Accordingly, this material is a functional material having functions of Mo and Cu in combination. By selecting the content ratio of these components and a microscopic or a microscopic arrangement design, it is possible to provide members having various functions and various functional levels.
The above-mentioned material is roughly classified into a material in which Mo and Cu particles are microscopically substantially uniformly distributed (type 1), a material in which Mo and Co are macroscopically bonded to each other (type 2), and a material comprising a combination of these types or having an intermediate arrangement therebetween (type 3).
The type 1 is a Mo—Cu based composite material in a narrow sense. The type 2 includes a material comprising a laminated structure of Cu and Mo, such as CMC (registered trademark) obtained by adhering Cu, Mo and Cu plates in this order, and a material in which Mo and Cu are macroscopically unevenly arranged. The type 3 is a mixture of these types.
The terms “Mo—Cu sintered alloy” and “Mo—Cu alloy phase” in the specification of Japanese Patent Application No. 2002-312130 which is a basis of the present application correspond to the above-mentioned original microscopic structure. In the present application, these terms are replaced by synonymous terms “Mo—Cu based composite material” and “Mo—Cu based composite phase”, respectively.
Hitherto, the above-mentioned material has been used mainly in a heat-sink member for releasing or radiating heat of an electrical or an electronic equipment, in particular, in a heat-sink member of a semiconductor apparatus. Since this material has the above-mentioned functions, it is possible to utilize advantageous properties of Mo and Cu, suppress disadvantageous properties thereof, and complement each other. Therefore, depending upon its material design, a number of applications are found. For example, it is conceivable to apply the material to a structural member if the rigidity of Mo and the ductility of Cu are utilized, to a member for a special radiation apparatus if radiation-resistant properties of Mo and Cu are utilized, to a heat-resistant electrical or electronic member, such as an electric contact and a discharge-machining or a welding electrode, if the heat resistance of Mo and the electroconductivity of Cu are utilized, and to a member for a chemical apparatus if chemical properties of Mo and Cu are utilized.
As regards the Mo—Cu based composite material suitable for the heat-sink member, particularly, to be mounted to a semiconductor device, Japanese Patent Publication (JP-B) No. H7-105464 (hereinafter referred to as a reference document 1) discloses an unrolled material of the type 1. Japanese Unexamined Patent Application Publications (JP-A) Nos. H6-310620 (hereinafter referred to as a reference document 2) and 2001-358266 (hereinafter referred to as a reference document 3) disclose a rolled material of the type 1. Japanese Patent (JP-B) No. 2000-323632 (hereinafter referred to as a reference document 4) discloses a material of the type 2 comprising Mo, Cu and Mo laminated in this order. Japanese Unexamined Patent Application Publication (JP-A) No. H10-12767 (hereinafter referred to as a reference document 5) discloses a material of the type 2 comprising Cu, Mo and Cu laminated in this order and another material of the type 3 comprising a Mo—Cu based composite material layer combined therewith.
As is well known, the material intended for the above-mentioned application or use is mainly required to have a high thermal conductivity during practical use and to be matched in thermal expansion coefficient with the semiconductor device and a peripheral member at the periphery of a mounting area of the semiconductor device (hereinafter referred to as an envelope member) during practical use and at the time of mounting. In the future, following a rapid increase in degree of integration of the semiconductor device, development of miniaturization of a large-capacity package, development of an increase in capacity of a rectifier of an electrical apparatus, and so on, it is expected that heat load on a member mounted to a package will rapidly increase. Accordingly, the heat-sink member is required to have a yet higher thermal conductivity. For example, in case where the semiconductor device is made of Si and the envelope member is made of AlN, the thermal expansion coefficients thereof are both small and close to that of Mo. In this event, it is difficult to increase the thermal conductivity and to achieve matching in thermal expansion coefficient only by adjusting the composition ratio of the whole of the Mo—Cu based composite material.
The materials disclosed in the reference documents 4 and 5 are well designed, for example, improved in lamination design of Mo and Cu and a connecting surface connected to a mating or counterpart member in order to achieve matching in thermal expansion coefficient with the mating member at the time of mounting and during practical use. However, because of a clad structure, interlayer thermal stress tends to be generated so that some deformation is inevitable in case where a high thermal load is applied at the time of mounting and during practical use.
The reference document 1 discloses the material which contains Mo and Cu substantially uniformly distributed microscopically in three-dimensional directions and which comprises a Mo—Cu based composite phase as a whole. A plastic-deformed material obtained by plastic deformation of the above-mentioned material is disclosed in the reference document 2. In the plastic-deformed material, component particles are stretch-oriented in a plastic-deformation direction, as described in the document. It is stated that, as compared with the material of the reference document 1 containing the same Cu amount, the thermal conductivity is substantially equivalent and the thermal expansion coefficient is lowered by about 1×10−6/° C. In this case, however, it is supposed that the thermal conductivity is equivalent to that in the reference document 1 in the plastic-deformation direction but is slightly lowered in a thickness direction. This also applies to the material in the reference document 3. As described above, the Mo—Cu based composite material is increased in thermal conductivity and thermal expansion coefficient in proportion to the Cu amount. Accordingly, there is a limit in increasing the thermal conductivity while suppressing the thermal expansion coefficient. Further, in the plastic-deformed material, these thermal characteristics exhibit directivity. It is therefore necessary to proceed with the material design also based on such directivity.
In the foregoing, the tendency of the conventional material design of the Mo—Cu based composite material has been reviewed in conjunction with the heat-sink member for the semiconductor apparatus by way of example. In case where development towards other applications is sought utilizing other functions of this material, it is also necessary to overcome the problem with the same concept. Specifically, if this material is used for a certain application, it is desired to achieve a novel material design such that advantageous functions of Cu and Mo as main components are utilized while disadvantageous functions thereof are suppressed or such that these components can be complemented by each other.
In view of the above, it is a first object of the present invention to provide composite materials of the type 1 and the type 2, capable of achieving a high thermal conductivity and matching in thermal expansion coefficient with an envelope member.
It is a second object of the invention to provide a composite material for a heat-sink member, considering heat-radiation properties after plastic deformation.
It is a third object of the invention to provide a composite material which can be matched in thermal expansion coefficient with Si and GaAs of a semiconductor device and various packaging materials, in particular, alumina and AlN and which is low in cost and has a high thermal conductivity adapted to a higher degree of integration and a lighter weight.
It is a fourth object of the invention to provide a heat-sink member using the above-mentioned composite material.
It is a fifth object of the invention to provide a method of producing the above-mentioned composite material.
It is a sixth object of the invention to provide a semiconductor apparatus in which the above-mentioned heat-sink member is used for heat radiation of a semiconductor apparatus, for example, in a heat-radiating substrate.